How to find the G-spot... Men, read this but keep it under your hats, it will put you way ahead of Joe Q. Badsex. That is, just about everyone else in America.
Assuming she is lying on her back, insert a finger into her, palm up, and make a come here motion along the top of her vaginal wall. That's it. Repeat until new levels of sexual extasy are reached for her.
Make sure she is well aroused and lubricated before you attempt this. Otherwise it may not do anything for her, or possibly hurt. I recommend moving onto this only after other activities or clitoral orgasm. It's most sensitive location varies slightly in some women but it's usually near the front just behind the pelvic bone. When aroused it may swell up slightly.
About safety: Make sure that your hands are clean - (wash them first!). Be careful of nails, keep them short and clean. If you use a lubricant be sure that it is water-based. K-Y Jelly will work but it gets sticky and gross. I recommend something like Astroglide if necessary.
If stimulated to g-spot orgasm, many women will excrete a white substance, similar in appearance to semen. If you get this, you did your job well. Congratulations. Behold the beauty you have unleashed in her.